First -- Carbohydrates

Second -- Fats

Third -- Protein

Carbohydrates:  45 to 65%

Fat:  20% to 35%

Protein:  10% to 35%

Dietary Reference Intakes - The US standards for the major nutrients.  They include recommendations for each gender and age group as well as recommendations for pregnancy and lactation.

The DRI's include the 4 interconnected categories:

1) Recommended Dietary Allowande (RDA).  This is the daily instake of a nutrient that meets the needs of almost all healthy individuals of specific age and gender.

2) Estimated Average Requirement (EAR). This is the intake level that meets the needs of half of the individuals in a specific groups.  

3) Adequate Intake (AI) The AI is used as a guide when not enough scientific evidence is available to establish the RDA figure.  Both the RDA and the AI may be used as goals for individual intake.

4) Tolerable Upper Intake Level (UL) This indicator is not recommended intake, but sets the maximal intake that is unlikely to pose adverse health risks in almost all heatlhy individuals.

Classes of Carbohydrates:

Simple Carbohydrates

monosaccharide - one sugar unit

Disaccharides have two sugar units

Complex Carbohydrates

polysaccharides - large, complex compounds of many saccharide units in long chains.  Complex forms of dietary carbohydrates are starch, which is digestible and provides a major energy source, and dietary fiber, which is indigestible (human beings lack the necessary enzymes) and thus provides important bulk in the diet.

Glucose - The basic single sugar in body metabolism circulating in the blood and is the primary fuel for cells..  The body supply mainly comes from the digestion of starch.

Fructose - mainly found in fruits, from which it gets its name, or in honey.  Fructose is the sweetest of the simple sugars.

Galactose - not found as a free monosaccharide in the diet; it mainly comes from the digestion of milk sugar, or lactose.

Sucrose = Glucose + Fructose

Lactose = Glucose + Galactose

Maltose = Glucose + Glucose

Sucrose = Glucose + Fructose

Lactose = Glucose + Galactose

Maltose = Glucose + Glucose

Sucrose - common table sugar.  consiting of glucose and fructose

Lactose - The sugar in milk, formed in mammary glands, is lactose.  Its two single-sugar units are glucose and galactose.  Lactose is the only common sugar not found in plants.  Lactose aids in the absorption of calcium and phosphorus.

Maltose - usually not found as such in the diet.  Glucose and glucose.  It is derived in the body from the intermediate digestive breakdown of starch.

Cellulose - the chief part of the framework of plants i.e. stalks and leaves of vegetables, outer covering of seeds.  It remains undigested in the GI tract and provides important bulk to the diet.  This bulk helps move the food mass along, stimulates normal muscle action in the intestine, and forms feces for elimination of waste products.  The main sources of cellulose are the stems and leaves of vegetables and the coverings of seeds and grains.  Holds water; reduces elevated colonic intraluminal pressure

Lignin - the only noncarbohydrate type of dietary fiber, is a large compound that forms the woody part of certain plants. i.e. broccoli stems and fruits with edible seeds, such as strawberries and flaxseeds. Antioxidant; binds bile acids, cholesterol, and metals.

Noncellulose Polysaccharides - hemicellulose, pectins, gums and mucilages, and algal substances are noncellulose polysaccharides.  They absorb water and swell to a larger bulk, thus slowing the emptying of the food mass from the stomach, binding bile acids, (including cholesterol) in the intestin, and preventing spastic colon pressure by providing bulk for normal muscle action. Noncellulose polysaccharides also provide fermentation material on which colon bacterial can work.

Primary Energy Function - provide fuel for the body

Special Tissue Functions - Glycogen reserves in the liver and muscle tissue provide a constant exchange with the body's overall energy balance system.  Carbohydrates help regulate both protein and fat metabolism.  If dietary carbohydrate is sufficient to meet general body energy needs, protein does not have to be broken down to supply energy.  Constant carbohydrate intake and reserves are necessary for proper functioning of the central nervous system (CNS)

The chewing of food, a process called mastication, breaks food into fine particles and mixes it with saliva (salivary enzyme - salivary amylase secreted by the parotid glands which lie under each ear at the back of the jaw.)

Chemical digestion of carbohydrate is completed in the small intestine by specific enzymes from both the pancreas and intestine.

it is not completely filled with all the hydrogen it can hold.  As a result it is less heavy and less dense.  One unfilled spot would be called a monounsaturated fat, such as olives and olive oil, peanuts and peanut oil, canola oil, almonds, pecans, and avocados.

If the component fatty acids have two or more unfilled spots, the fat is called a polyunsaturated fat.  Examples of such fats, in order of their degree of unsaturation are the vegetable oils:  safflower, corn, cottonseed, and soybean.  Fats from plant and fish sources usually are unsaturated.

Amino acids are joined in unique chain sequences to form specific proteins.

Each amino acid is joined by a peptide bond.  Two amino acids joined together are called a dipeptide bond.

Indispensable Amino Acids - Nine amino acids are classified as indispensable because the body cannot manufacture them in sufficient quantity or at all and they are necessary in the diet and cannot be left out.

Dispensable Amino Acids - Five amino acids that the body can synthesize from other amino acids provided the necessary building blocks and enzymes are present.  These amino acids are needed by the body for heatlhy life but are dispensable (not necessary) in the diet.

Conditionally Indispensable Amino Acids - The remaining six amino acids are classified as conditionally indispensable.  Under certain physiologic conditions these amino acids, which are normally synthesized in the body like the dispensable amino acids, must be consumed in the diet.  Arginine, cysteine, glutamine, glycine, proline, and tyrosine are indispensable when endogenous sources cannot meet the metabolic demands.  For example, the human body can make cystein from the genetic disorders also may render an amino acid condtionally indispensable.

Lacto-ovo-vegetarians:  Vegetarians who follow a food pattern that allows dairy products and eggs.  

Lacto-vegetarians:  These vegetarians accept only dairy products from animal sources to complement their basic diet of plant foods.  The use of milk and milk products (e.g. cheese) with a varied mixed diet of whole or enriched grains, legumes, nuts, seeds, fruits, and vegetables in sufficient quantities to meet energy needs provides a balanced diet.

ovo-vegetarians:  The only animal foods included in the ovo-vegetarian diet are eggs.

Vegans:  Vegans follow a strict vegetarian diet and consume no animal foods.

Trypsin - secreted first as inactive trypsinogen, is activated by the enzyme enterokinase.  Enterokinase is secreted from the intestinal cells on contact with food entering the duodenum, the first section of the small intestine.  

Chymotrypsin - secreted frist as the inactive chymotrypsinogen, is activated by the trypsin already present.  The active enzyme then continues the sam eprotein-splitting action of trypsin.

Carboxypeptidase - attacks the acid (carboxyl) end of the peptide chains, producing small peptides and some free amino acids.  Carbosypeptidase also is first released as the inactive proenzyme procarboxypeptidase and is activated by trypsin.

Aminopeptidase - attacks the nitrogen-containing (amino) end of the peptide chain and releases amino acids one at a time, producing peptides and free amino acids.

Dipeptidase - the final ennzyme in the protein-splitting system, completes the large task by breaking the reamining dipeptides into two free amino acids.  This finely coordinately system of protein-splitting enzymes breaks down the large, complex proteins into progressively smaller peptide chains and frees each individual amino acid.  The free amino acids are now ready to be absorbed directly into the portal blood circulation for use in building body tissues.

Chemical Score (CS):  derived from the amino acid pattern of the food.  A high-quality protein food, such as an egg (with a  value of 100) is compared with other foods according to their amino acid ratios.

Biological value (BV):  based on nitrogen balance.

Net protein utilization (NPU):  based on the biologic value and the degree of the food protein's digestibility.

Protein efficiency ratio (PER):  based on the weight gain of a growing test animal in relation to its protein intake.

Children and adults should get 10% to 35% of their caloric intake from protein.

The RDA for both men and women is set at 0.8 g of high-quality protein per kilogram of desirable body weight per day.

Needs are higher for infants, pregnant and breastfeeding women, and possibly vegans.

Severe physical stress, such as illness, disease, and surgery can increase a person's need for protein

Body cells cannot use food as it is eaten.  Food must be changed into simpler substances for absorption and then into even simpler substances that cells can use to sustain life.  Preparing food for the body's use involves many steps including:

Digestion, absorption, transport, and metabolism

Beginning in the mouth, muscles and nerves in the walls of the GI tract coordinate their actions to provide the necessary motility for digestion to proceed.  Motility is the ability to move spontaneously.  Muscles - layers of smooth muscle in the GI wall interact to provide two general types of movement:  (1) muscle tone, or tonic contraction, which ensures continuous passage of the food mass and valve control along the way: and (2) periodic muscle contraction and relaxation, which are rhythmical waves that mix the food mass and move it forward.  These alternating muscular contractions and relaxations that force the contents forward are known as peristalsis,

Nerves.  Specific nerves regulate muscle action along the GI tract.  A complex network of nerves in the GI wall extends from the esophagus to the anus.  This network is called the intramural nerve plexus.  These nervves do three things:  (1) control muscle tone in the wall, (2) regulate the rate and intensity of the alternating muscle contractions, and (3) coordinate all the various movements.

A number of secretions work together to make chemical digestion possible.  Five types of substances generally are involved:

Hydrochloric Acid and Buffer Ions - Hydrochloric acid and buffer ions are needed to produce the correct pH necessary for enzyme activity

Enzymes - digestive enzymes are proteins, specific in kind and quantity for breaking down nutrients.

Mucus - Secretions of mucus lubricate and protect the mocosal tissues lining the GI tract as well as help mix the food mass. 

Water and Electrolytes - the products of digestion are carried and circulated through the GI tract and into the tissues by water and electrolytes

Bile - made in the liver and stored in the gallbladder, bile divides fat into smaller pieces to expose more surface area for the actions of fat enzymes.  (liver can compensate if gallbladder is removed)

The gastric secretions contain three types of materials that aid chemical digestion in the stomach:

Acid - parietal cells within the lining of the stomach secrete hychochloric acid to create the necessary degree of acidity for gastric enzymes to work.  hydrochloric acid also works on denaturing proteins in the stomach

Mucus - mucous secretions protect the stomach lining from the erosive effect of hydrochloric acid.  Secretions also bind and mix the food mass and help move along.

enzymes - The inactive enzyme pepsinogen is secreted by stomach cells and is activated by hydrochloric acid to become the protein-splitting enzyme pepsin.  Other cells produce small amounts of a specific gastric lipase called tributyrinase, which works on tributyrin (butterfat), but this is a relatively minor activity in the stomach.  Anger and hostility increase secretions.  Fear and depression decrease secretions and inhibit blood flow and motility.

Up to this point, digestion of food has largely been mechanical, delivering a semifluid mixture of fine food particles and watery secretions to the small intestine.  Under the control of nerve impulses, walls stretch from the food mass or hormonal stimuli, and the intestinal muscles produce several types of movement that aid digestion as follows:

Peristaltic waves slowly push the food mass forward

Pendular movements from small, local muscles sweep back and forth, stirring the chyme at the mucosal surface

Segmentation rings from the alternating contraction and relaxation of circular muscles progressively chop the food mass into successive soft lumps and mix them with secretions.

Longitudinal rotation by long muscles running the length of the intestine, rolls the slowly moving food mass in a spiral motion, mixing it and exposing new surfaces for absorption

surface villi motions stir and mix the chyme at the intestinal wall, exposing additional nutrients for absorption.

The pancreas and intestines secrete enzymes specific for the digestion of carbohydrates, proteins, and fat.

Pancreatic Enzymes

1) Carbohydrate:  Pancreatic amylase converts starch to the disaccharides maltose and sucrose.

2) Protein:  Trypsin and Chymotrypsin split large protein molecules into smaller and smaller peptide fragments and finally into single amino acids, carboxypeptidase removes end amino acids from peptide chains.

3) fat:  Pancreatic lipase converts fat to glycerides and fatty acids.

Intestinal Enzymes

1) Carbohydrate:  disaccharidases (maltase, lactase, and sucrase) convert their respective disaccharides (maltose, lactose, sucrose) to monosacchharides (glucose, galactose, and fructose).  A large percent of the world's population does not produce enough lactase to digest lactose

2) Protein:  The intestinal enzyme enterokinase activates trypsinogen (from the pancreas) to become the protein-splitting enzyme trypsin.  Amino peptidase removes end amino acids from polypeptides.  Dipeptidase splits dipeptides into their two remaining amino acids

3) Fat:  Intestinal lipase splits fat into glycerides and fatty acids.

Mucus

Large quantities of mucus, secreted by intestinal glands, protect the mucosal lining from irritation and erosion caused by the highly acidic gastric contents entering the duodenum.

Bile

Bile is an emulsifying agent and an important aid to fat digestion and absorption.  It is produced by the liver and stored in the adjacent gallbladder, ready for use when fat enters the intestine.

Hormones

The hormone secretin produced by the mucosal glands in the first part of the intestine, controls the acidity and secretion of enzymes from the pancreas.  The hormone cholecystokinin, secreted by intestinal mucosal glands when fat is present, triggers the release of bile from the gallbladder to emulsify fat.

Bile production (for fat digestion)

Synthesis of proteins and blood clotting factors

metabolism of hormones and medications

Regulation of blood glucose levels

Urea production (to remove waste products of normal metabolism)

Mucosal folds:  Like the hills and valleys of a mountain range, the surface of the small intestine piles into many folds.  Mucosal folds can easily be seen when such tissue is examine.

Villi:  Closer examination under a regular light microscope reveals small, fingerlike projections, the villi, covering the piled-up folds of mucosal lining.  These little villi further increase the area of exposed surface.  Each villus has an ample supply of blood vessels to receive protein and carbohydrate materials as well as a special lymph vessel to receive fat materials

Microvilli:  Even closer examination with an electron microscope reveals a covering of smaller projections on the surface of each tiny villus.  The covering of microvilli on each villus is called a brush border because it looks like bristles on a brush.

Simple diffusion is the force by which particles move outward in all directions from an area of greater concentration to an area of lesser concentration. 

Facilitated diffusion is similar to simple diffusion but uses a protein channel for carrier-assisted movement of larger items across the mucosal cell membrane.

Active transport is the force by which particles move against their concentration gradient.  Active transport mechanisms usually require some sort of carrier partner to help ferry the particles across the membrane.  For example, glucose enters absorbing cells through an active transport mechanism involving sodium (Na⁺) as a ferrying partner.

Pinocytosis is the penetration of larger materials by attaching to the thicker cell membrane and being engulfed by the cell.

The mitochondria of the cell is the work center in which all metabolic reactions take place.  The two types of metabolism are catabolism and anabolism.  Catabolism is the breaking down of large substances into smaller units.  Anabolism is the opposite, it is the process by which cells build large substances from smaller particles, such as building a complex protein from single amino acids within the body.

The combined processes of metabolism ensure that the body has much needed energy in the form of adenosine triphosphate (ATP).

The body needs constant energy to do work necessary for maintenance of life and health.  Voluntary work is the actions related to a person's usual activities as well as any additionhal physical exercise.

Involuntary work includes all activities in the body not consciously performed.  These activities include such vital processes as circulation, respiration, digestion, and absorption (referred to as the thermic effect of food) as well as many other internal activities that maintain life.

Measuring Basal Metabolic Rate or Resting Metabolic Rate

(BMR or RMR)

A measure of basal metabolic rate (BMR) or RMR is sometimes made in clinical practice (e.g. on metabolic wards or research laboratories) using indirect calorimetry.  This method indirectly measures the amount of energy a person uses while at rest.

Predicting BMR or RMR

1 kal x kg body weight x 24 hours

convert pounds to kilograms:  154lbs/2.2 = 70kg

1 kcal x 70 kg x 24 hr = 1680 kcal/24 hrs